ASTM E1270-88(2003)
(Test Method)Standard Test Method for Equal Arm Balances
Standard Test Method for Equal Arm Balances
SIGNIFICANCE AND USE
This test method should enable the user of the balance to interpret data determined thereon in terms of accuracy and precision. It should be helpful in using a particular instrument to best advantage. Weaknesses as well as strengths should become apparent. It is not the intention of this test method to compare similar instruments of different manufacture but rather to assist in choosing an instrument which will meet the needs of the user.
SCOPE
1.1 This test method can be used for testing equal-arm balances of any capacity and sensitivity. The testing procedure should enable the user to characterize his instrument sufficiently to determine whether or not it is suitable for the purpose for which it is to be used.
1.2 The characteristics to be examined include:
1.2.1 Sensitivity at all loads,
1.2.2 Lever arm ratio,
1.2.3 Damping ratio (for instruments without accessory dampers),
1.2.4 Period of oscillation,
1.2.5 Precision, and
1.2.6 Linearity and calibration of accessory devices that provide on-scale indication of weight.
1.3 This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E1270–88(Reapproved2003)
Standard Test Method for
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Equal Arm Balances
This standard is issued under the fixed designation E1270; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method is designed to test balances whose lever-arm ratio is substantially equal to unity.
Although largely superseded by new technologies, equal-arm balances retain a special niche for very
high precision weighing of larger samples (usually greater than 1 kg) as well as objects with large
buoyancy (such as gas bottles). Balances of this type can range from simple instruments of moderate
precision (1:10000) to extremely high precision devices with precision of 1:10000000 or better. A
number of accessory devices may be included for assisting in the weighing process. These devices
may contribute to errors as well as can the basic lever mechanism.This method is designed to test the
entire instrument including the accessories.
1. Scope 3.1.1 capacity—maximumloadrecommendedbythemanu-
facturer. Usually, the capacity refers to the maximum load on
1.1 This test method can be used for testing equal-arm
each pan simultaneously.
balances of any capacity and sensitivity. The testing procedure
3.1.2 readability—value of the smallest unit of weight
should enable the user to characterize his instrument suffi-
which can be read. This may include the estimation of some
cientlytodeterminewhetherornotitissuitableforthepurpose
fraction of a scale division or, in the case of a digital display,
for which it is to be used.
will represent the minimum value of the least significant digit.
1.2 The characteristics to be examined include:
3.1.3 sensitivity—smallest value of weight which will cause
1.2.1 Sensitivity at all loads,
a change of indication which can be determined by the user.
1.2.2 Lever arm ratio,
This may be independent of the readability because of the
1.2.3 Damping ratio (for instruments without accessory
choice of the reading device used. For example, a magnifying
dampers),
glass may be used in conjunction with a reading scale to
1.2.4 Period of oscillation,
observe a sensitivity not readily determined without the mag-
1.2.5 Precision, and
nifying glass.
1.2.6 Linearity and calibration of accessory devices that
3.1.4 precision—repeatabilityofthebalanceindicationwith
provide on-scale indication of weight.
the same load under essentially the same conditions.The more
1.3 This standard does not purport to address all of the
closelythemeasurementsaregrouped,thesmallertheindexof
safety concerns associated with its use. It is the responsibility
precision will be. The precision should be measured under
of the user of this standard to establish appropriate safety and
environmental conditions that represent the conditions under
health practices and determine the applicability of regulatory
which the balance is normally used.
limitations prior to use.
3.1.5 accuracy—degree of agreement of the measurement
2. Referenced Documents
with the true value of the magnitude of the quantity measured.
3.1.6 linearity—characteristic of a direct reading device. If
2.1 ASTM Standards:
a device is linear, calibration at 2 points (for example, 0 and
E617 Specification for Laboratory Weights and Precision
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full-scale) calibrates the device (for example, 2 points deter-
Mass Standards
mine a straight line); if a device is nonlinear, additional points
3. Terminology
are needed (perhaps a great many).
3.1.7 standard weight—any weight whose mass is given.
3.1 Definitions of Terms Specific to This Standard:
Since weights are not always available with documented
corrections, weights defined by class (see Specification E617)
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This test method is under the jurisdiction of ASTM Committee E41 on
may be used if the class has sufficiently small tolerance limits
Laboratory Apparatus and is the direct responsibility of Subcommittee E41.06 on
and there is an understanding that errors perceived as being
Weighing Devices.
instrumental could be attributed to incorrectly adjusted
Current edition approved Sept. 30, 1988. Published November 1988.
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Annual Book of ASTM Standards, Vol 14.02. weights.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E1270–88 (2003)
3.1.8 off-center errors—differences in indicated weight instrument in a controlled environment, it may be necessary to
when a sample is shifted to various positions on the weighing allow 24 h for such equilibrium.
area of the weighing pan. No separate test is described. 7.
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